Discharge tube



Nov. 3, 1936. H. ROTl-|E 2,059,810

DI SGHARGE TUBE Filed May 18, 1954 INVENTOR ATTORNEY Patented Nov. 3, 1936 PATENT OFFICE DISCHARGE TUBE Horst Rothe, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic m. b. H, Berlin, Germany, a corporation of Germany Application May 18, 1934, Serial No. 726,211 In Germany February 6, 1933 1 Claim.

It is known that the mutual conductance of a discharge tube can be increased by disposing or mounting the control grid electrode as close to the cathode or filament as possible. In order that, in spite of such arrangement, the field distribution in the vicinity of the filament may be uniform, it is moreover necessary that the grid electrode should be made as close-meshed as possible. In order that the other electrodes located posteriorly of the control electrode may under these circumstances possess a still sufficiently high transgrid action across the control grid,

their distances from the latter must also bechosen small. However, a minimum limit is approached in so far as the wider turns, with a view to insuring mechanical solidity, are attached to supporting wires located as a general rule outside the grid surface. Then again, in order that Y the tendency for the tube to become microphonic may be reduced, 9. condition ascribable to elastic deformations of the electrodes due to shocks and percussions, the said supporting stays are made particularly stout, and this requires an undesirably great inter-electrode distance.

Now, in order that the active electrode surfaces may still be approached as much as possible, the suggestion is here made to provide the electrodes following the control electrode with enlarged or bulged portions for the accommodation of the supporting stays and to have the rest of the electrode shell or circumference conform to or arranged parallel to the cathode surface. In this manner it is possible to reduce the distances between the active parts of the electrode surfaces to a considerable extent.

The basic idea of the invention therefore is to create a form of electrode in which the active parts of all similarly shaped electrodes are equidistant so that maximum slope is insured, and wherein the supporter stays and the stiffening fins no longer mean an impediment in the choice or fixing of the inter-electrode distance, and wherein the unavoidable field distortion is minimized.

The invention willbe described in more detail by reference to the accompanying drawing which discloses several modifications. Fig. 1 shows schematically a cross-section through the electrode system of a triode tube comprising a circular cathode K and a control grid G which is supported by twostay wires S. The anode or plate A has two trough-shaped bulges which embrace the supporting stays S of the control grid G and which at the same time may serve for the accommodation of the supports S of the anode itself. The rest of the anode circumference is of circular shape. It can be readily seen that the distance of these parts from the control grid is much smaller than in a case where the plate is fully cylindrical. In a similar manner a screen grid SG when interposed between the control grid G and the plate A would take a similar shape, as shown in Fig. 3.

Fig. 2 represents a similar form of construction in which the supporting wires S of the control grid G are made especially stout for the object of diminishing the tendency to ring. The invention could be analogously applied also when the cathode does not form a circular cylinder but presents an oval or an elliptic cross-sectional form with any desired curvature of bend along its periphery or else the shape of a prism.

The invention is valuable also for such discharge tubes in which secondary space charges are set up as is true, for instance, of a spacecharge grid type of tube. So far as the controlled discharge process is concerned it is then the virtual cathode formed by the space-charge that should be regarded as the source of electrons rather than the surface of the heated cathode. The formation of a space-charge being as uniform as feasible and produced in a definite location, is greatly promoted by choosing forms for the electrodes as here disclosed.

In the standardized manufacture of electron tubes, the step here disclosed, namely, of providing bulges for the accommodation of the grid stays, insures this additional advantage that the distance of the attachment points of the various supporting stays maybestandardized so that only a single sort of supporting element need to be manufactured and kept in stock. The distance prescribed for the various types between the active electrode surfaces can be chosen quite independently of the distance of the supporting stays.

What is claimed:

An electron discharge tube comprising a cathode having a cylindrically-shaped emitting surface, a similarly shaped control grid surrounding the cathode, a pair of support rods for said grid spaced apart a greater distance than the grid diameter and extending parallel to its axis, and at least one additional electrode completely surrounding the control grid and provided with a pair of support rods arranged in alignment with the grid support rods, said additional electrode having outwardly extending longitudinal channels, oval-shaped in cross-section for housing both sets of support rods, the remaining portions of said electrode between the channeled portions being substantially cylindrical and arranged in concentric relation with the control grid.

HORST ROTHE. 

